Fluorescence probe for D-glucose and beta-glucosidase based on anthraquinone imidazole fluorophores

Abstract

The anthaquinone derivatives containing boronic acid or glycoside as an active site were synthesized and characterized by spectroscopy. We have developed the boronic anthaquinone based sensors (OB and PB) for glucose sensing by the enzymatic probe system with glucose oxidase. Actually, the glucose oxidase can react with glucose and oxygen to generate the gluconic acid and hydrogen peroxide. In consistent with our hypothesis, the generated H₂O₂ can convert the boronic moiety of sensors to be hydroxyl group resulting in the fluorescence quenching of sensor OB. The advantage of this sensor is that it can detect glucose specifically. The kinetic of this process measured by Michaelis-Menten constant (Km) provided the Km values of 0.174 mM, indicating that OB exhibits a higher affinity for glucose oxidase. The limit of detection (LOD) of glucose for OB evaluated in the range of 0.08-0.42 mM of glucose by the spectrofluorometry was 0.0114 mM. Moreover, the glycoside anthaquinone based sensors (OAG and PAG) bearing the anthraquinone as a sensory unit and glucoside as a active site were synthesized to detect β-glucosidase. After adding β-glucosidase, the fluorescence decreases of PAG were observed due to the cleavage of O-glucoside. The results showed that PAG can be a sensor for determining β-glucosidase in enzymatic probe system with the observation of fluorescence change. To improve the sensitivity of PAG for β-glucosidase sensing, we have applied PAG in the micellar system using CTAB as surfactant for enzymatic probe. This micellar system could reduce background signal from β-glucosidase and enhance the emission signal of PAG. Therefore, PAG in the micellar system can serve as a high potential for the β-glucosidase sensing. Finally, we tried to apply PAG in surfactant/lanthanide nanoparticles. The results also exhibited the enhancement of emission band of PAG in lanthanide nanoparticles and after adding β-glucosidase, the fluorescence intensity of PAG was significantly quenched. All approaches are exemplified by their application to develop a novel and highly sensitive fluorescence probe for β-glucosidase, which is widely used as the reporter of enzymes.